Muzzle blast from guns and rockets as well as blast from detonation of bare charges represent substantial noise pollution sources. This problem is especially severe in military installations where residential encroachment places neighbors relatively close to sites where test firing is necessary. Furthermore, high blast and noise levels may pose physiological and/or psychological problems for the firing crew in field use.
In the past, mechanical devices such as silencers have been used to reduce the muzzle blast from guns. Such silencers are designed to slowly release the pressure of the propellent gases after the propellent gases have completed their task of accelerating the projectile. Silencers unfortunately weigh a significant fraction of the overall gun weight and have physical dimensions which may, in fact, exceed the physical dimensions of the gun barrel. In small caliber applications, the weight, although providing inconvenience, may be tolerable.
Although they may be acceptable in proving ground applications where large blast suppressors may be permanently mounted, the size and weight penalty of mechanical silencers are not acceptable for field use with large caliber weapons in a modern highly mobile military environment where survivability requires rapid movement from firing position to firing position.
An alternative to mechanical silencers for blast reduction includes placing a mass of aqueous foam surrounding, and forward of, the muzzle of the weapon. This technique requires a confinement device of some sort which may be filled with the aqueous foam from a foam generator prior to weapon firing. The foam acts to quench the strength of the blast through mechanisms which are not definitely established. The requirement for a foam generation system and a mechanical confinement apparatus reduces the attractiveness of such a technique. No foam system of blast suppressions are currently known to have been developed to a practical condition.
Rocket devices also have blast and noise over-pressure problems particularly in the case of shoulder-fired rockets. The blast and noise over-pressure levels may reach limits which produce psychological or physiological harm to the firing crew. Of the methods previously employed to reduce the blast and noise over-pressure reaching the firing crew, virtually all involve addition of material to the weapon system. If a weapon which is nominally man portable increases in weight significantly, it loses its field utility since it no longer can be carried and served.
Blast suppression from bare charge detonation has typically taken the form of heavy steel mesh matting or heavy baffling plates and walls to provide mechanical constraint of the bare charge blast. Aqueous foam suppression has also been used in this application. As in the applications previously discussed, foam suppression requires a containment vessel and a foam generator.